The present invention relates in general to automotive sound systems and, more specifically, to a distributed multiprocessor-based architecture for improving manufacturability of such sound systems.
With the recent introduction of digital audio technology, automobile consumers have been given a selection of automotive sound systems. Thus, a typical system comprises an AM/FM radio receiver combined with a standard cassette tape Player, a digital compact disc (CD) player, or a digital audio tape (DAT) player.
Prior art systems have been designed and manufactured separately according to whether the system is a radio receiver/cassette, a radio receiver/CD, or a radio receiver/DAT. With the advent of electronic radio tuning, digital displays, station search functions, etc., designers have come to rely heavily on the microcontroller. Thus, a microcontroller has been given control of radio functions and tape or CD functions in sound systems designed as integral units.
For example, U.S. Pat. No. 4,292,467, granted to Odlen et al., discloses an audio receiver in which level setting switches are monitored by a microprocessor. Level changes are loaded into memory, displayed to a user, and implemented by the microprocessor.
Component sound systems are also known wherein system parts, such as a radio, an amplifier, and a cassette tape player, are constructed as separate integral components which are interconnected during installation into an automobile. The separate components may each be microprocessor controlled.
The foregoing prior art systems have disadvantages in both design and manufacture. The integral units suffer from high cost due to the need for separate design efforts and different manufacturing operations. Thus, the manufacture of integral units has not been able to achieve full economy of scale. Component systems suffer these same disadvantages in addition to the disadvantage that they require larger dedicated packaging space in the automobile than integral units.
Burke et al., U.S. Pat. No. 4,637,022, discloses a mobile transmit/receive radio having a distributed processing environment. A shared bus links processors internally and externally. A structured subsystem interface is provided such that processors may be added to the system without changing the main control processor. Each processor is modelled as a set of registers which can transmit data to and receive data from the control processor. Therefore, each local processor requires nonshared connections to its peripheral devices. Such a system is undesirable from a manufacturing standpoint due to increased parts count, increased complexity, and reduced reliability. Furthermore, the register approach in Burke et al. is not readily adaptable to existing microprocessor controlled audio sound systems because the addressing and commanding of the multiprocessors requires the development of a new instruction set resulting in added design costs.